1. Download ngrok

The first step is to download a program to expose localhost or
another url behind a firewall to the Internet. We'll use ngrok which is a
program can be downloaded for free and
available for all major operating systems.

2. Start ngrok

The next step is to expose your web service. If your web service is on
localhost, simply run the following on the command-line:

$ ngrok http 3000

If you need to point ngrok to another host behind a firewall
(e.g. inside an intranet), use the full host instead of a port only:

$ ngrok http internal.host:8099

You should see a line that looks something like this:

Forwarding http://7e9ea9dc.ngrok.io -> 127.0.0.1:3000

or

Forwarding http://7e9ea9dc.ngrok.io -> internal.host:8099

Copy the *.ngrok.io URL to your clipboard or write it down.

Testing a host that is not localhost

If the web service you are trying to test is using another host that's
not localhost, for example http://private.behind-firewall.com, you
can make a tunnel by customizing the ngrok command using the
-host-header command-line flag: